Monroe Power Plant 

Monroe, Michigan 

Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

Conducted by: 

Steven Klafka, P.E., BCEE 

Wingra Engineering, S.C. 

Madison, Wisconsin
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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1. Introduction 

Wingra Engineering, S.C. was hired by Sierra Club to conduct an air modeling impact analysis to 

help the U.S. Environmental Protection Agency (USEPA), state and local air agencies identify 

facilities that are likely causing exceedances of the 1-hour sulfur dioxide (SO2) national ambient air 

quality standard (NAAQS). This document describes the results and procedures for an evaluation 

conducted for the Monroe Power Plant located in Monroe, Michigan. 

To ensure the modeling analysis reflected the cumulative concentration of SO2 emissions, it included 

emissions from the following additional sources of SO2 emissions located within 50 kilometers of 

the Monroe Power Plant: 

 River Rouge Power Plant - River Rouge, Michigan 

 Trenton Channel Power Plant - Trenton, Michigan 

 City of Wyandotte Municipal Power Plant - Wyandotte, Michigan 

 J.R. Whiting Plant - Erie, Michigan 

 Bay Shore Plant - Oregon, Ohio 

 U.S. Steel Great Lakes Works - Ecorse, Michigan 

The dispersion modeling analysis predicted ambient air concentrations for comparison with the 1-

hour SO2 NAAQS. The modeling was performed using the most recent version of AERMOD, 

AERMET, and AERMINUTE, with data provided to Sierra Club by regulatory air agencies or 

obtained through other publicly-available sources as documented below. The analysis was 

conducted in adherence to all available USEPA guidance for evaluating source impacts on 

attainment of the 1-hour SO2 NAAQS via aerial dispersion modeling, including the AERMOD 

Implementation Guide; USEPA's Applicability of Appendix W Modeling Guidance for the 1-hour 

SO2 National Ambient Air Quality Standard, August 23, 2010; modeling guidance promulgated by 

USEPA in Appendix W to 40 CFR Part 51; USEPA’s March 2011 Modeling Guidance for SO2

NAAQS Designations;1

 and, USEPA’s December 2013 SO2 NAAQS Designations Technical 

Assistance Document.2 

It was determined that based on either current allowable emissions or measured actual emissions, the 

Monroe Power Plant is estimated to create downwind SO2 concentrations which exceed the 1-hour 

NAAQS. 

 

 

1

 http://www.epa.gov/scram001/so2_modeling_guidance.htm 2

 http://www.epa.gov/oaqps001/sulfurdioxide/pdfs/SO2ModelingTAD.pdf 
Evaluation of Compliance with the 1-hour NAAQS for SO2

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2. Compliance with the 1-hour SO2 NAAQS 

2.1 1-hour SO2 NAAQS 

The 1-hour SO2 NAAQS takes the form of a three-year average of the 99th percentile of the annual 

distribution of daily maximum 1-hour concentrations, which cannot exceed 75 parts per billion 

(ppb).3

 Compliance with this standard was verified using USEPA’s AERMOD air dispersion model, 

which produces air concentrations in units of μg/m3

. The 1-hour SO2 NAAQS of 75 ppb equals 

196.2 μg/m3, and this is the value used for determining whether modeled impacts exceed the 

NAAQS.4

 The 99th percentile of the annual distribution of daily maximum 1-hour concentrations 

corresponds to the fourth-highest value at each receptor for a given year. 

2.2 Modeling Results 

Modeling results for Monroe Power Plant, five other power plants, and one industrial facility are 

summarized in Table 1. Results are provided for the Monroe Power Plant alone, and for all facilities 

combined. It was determined that based on either current allowable emissions or measured actual 

emissions, the Monroe Power Plant is estimated to create downwind SO2 concentrations which 

exceed the 1-hour NAAQS. 

More specifically, the modeling results presented in Table 1, show exceedances of the NAAQS by 

the plant’s allowable and actual emissions. “Allowable” is the peak emission rate from each unit as 

approved by the current air quality operation permit for the facility. The allowable emission results 

are for the six power plants and do not include those from the industrial facility, US Steel. 

For the six power plants, “actual” are the measured emissions for each hour between January 1, 2012 

and December 31, 2014 as taken from USEPA Air Markets Program Data.

5

 For US Steel, actual 

emissions are the annual average of emissions reported for calendar year 2014. 

In addition, the emissions from the other six facilities significantly contribute to the ambient SO2

concentration in the area impacted by Monroe Power Plant. 

Air quality impacts in Michigan are based on a background concentration of 2.6 μg/m3. This is the 

2011-13 design value for Wayne County, Michigan - the lowest measured background concentration 

in the state. This is the most recently available design value. See Section 5 for further discussion of 

 

3 USEPA, Applicability of Appendix W Modeling Guidance for the 1-hour SO2 National Ambient Air Quality Standard, 

August 23, 2010.

4 The ppb to μg/m3

 conversion is found in the source code to AERMOD v. 14134, subroutine Modules. The conversion 

calculation is 75/0.3823 = 196.2 μg/m3. 5

 http://ampd.epa.gov/ampd/ 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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the background concentrations used for this analysis. 

Table 1 - SO2 Modeling Results for Monroe Power Plant Modeling Analysis 

Emission Rates Facility 

99th Percentile 1-hour Daily Maximum (μg/m3

) Complies with 

NAAQS? Impact Background Total NAAQS 

Allowable 

Monroe 

220.8 2.6 223.4 196.2 No 

Actual 281.3 2.6 283.9 196.2 No 

Allowable All Facilities 

without 

Whiting 

272.3 2.6 274.9 196.2 No 

Actual 289.2 2.6 291.8 196.2 No 

Allowable 

All Facilities 

551.6 2.6 554.2 196.2 No 

Actual 289.9 2.6 292.5 196.2 No 

The emissions used for the modeling analysis are summarized in Table 2. 

Based on the modeling results, Table 3 provides the emission reductions from current allowable 

rates necessary to achieve compliance with the 1-hour NAAQS. This assumes a one-hour averaging 

period for the emission rate and that the emission rate is binding at all times. However, given the 

conservative aspects of this modeling protocol, it is extremely likely that this limit is too high to 

protect the NAAQS. For example, startup or shutdown periods were not evaluated. During these 

periods, decreased gas velocities and temperatures may lead to greater ambient impacts at ground 

level. Further, the hypothetical emission limitation in Table 3 would allow Monroe Power Plant to 

consume the entire NAAQS, leaving little to no room for any other source of SO2 in the area. No 

margin of safety has been included in the hypothetical emission limitation. 

Predicted exceedances of the 1-hour NAAQS for SO2 based on allowable emissions extend 

throughout the region to a maximum distance of 50 kilometers. 

Figure 1 shows the extent of NAAQS violations based on allowable emissions from all six power 

plants. 

Figure 2 shows the extent of NAAQS violations based on actual hourly emissions from all facilities. 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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Table 2 - Modeled SO2 Emissions 6

Stack 

ID 

Unit 

ID 

Allowable Emissions 

(lbs/hr) 

Actual Emissions 

(lbs/hr) 

M01 Unit 1 2,462.6 2012-14 CEM 

M02 Unit 2 2,462.6 2012-14 CEM 

M03 Unit 3 2,462.6 2012-14 CEM 

M04 Unit 4 2,462.6 2012-14 CEM 

Monroe Facility Subtotal 9,850.2 2012-14 CEM 

Bay Shore - B01 Unit B006 1,897.6 2012-14 CEM 

R02 Unit 2 3,807.6 2012-14 CEM 

R03 Unit 3 4,458.9 2012-14 CEM 

River Rouge Facility Subtotal 8,266.5 2012-14 CEM 

T01 

Unit 16 907.2 2012-14 CEM 

Unit 17 907.2 2012-14 CEM 

Unit 18 907.2 2012-14 CEM 

Unit 19 907.2 2012-14 CEM 

Stack Subtotal 3,628.8 2012-14 CEM 

T02 Unit 9 8,984.8 2012-14 CEM 

Trenton Channel Facility Subtotal 12,613.6 2012-14 CEM 

W07 Boiler 07 390.0 2012-14 CEM 

W08 Boiler 08 183.0 2012-14 CEM 

Wyandotte Facility Subtotal 573.0 2012-14 CEM 

J01 Boiler 1 1,900.0 2012-14 CEM 

J02 Boiler 2 2,100.0 2012-14 CEM 

J03 Boiler 3 2,400.0 2012-14 CEM 

JR Whiting Facility Subtotal 6,400.0 2012-14 CEM 

SV0003 Coke Battery - 18.8 

SV0007 Hot Strip Mill - 195.3 

SV0013 A Furnace BFG Flare - 38.7 

SV0017 D Furnace Baghouse - 14.1 

SV0018 D Furnace Stove - 123.0 

SV0025 No. 2-1 Boiler - 126.6 

US Steel Facility Subtotal 516.5 

 

6

 Monroe allowable emissions were taken from MDEQ, Renewal Operating Permit MI-ROP-82816-2009a, July 25, 

2011. Bay Shore Plant allowable emissions were taken from OEPA, Final Air Pollution Control Title V Permit, 

P0105130, June 24, 2014. River Rouge allowable emissions were taken from MDEQ, Renewal Operating Permit MIROP-B2810-2012, April 1, 2012. Trenton Channel Power Plant allowable emissions were taken from MDEQ, Renewal 

Operating Permit 199600204, September 22, 2003. Wyandotte Municipal Power Plant allowable emissions were taken 

from MDEQ, Renewal Operating Permit MI-ROP-B2132-2010, April 15, 2010. J.R. Whiting Plant allowable emissions 

were taken from MDEQ, Renewal Operating Permit MI-ROP-B2846-2013, July 1, 2013. 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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Table 3 - Required Emission Reductions from Monroe Power Plant for Compliance with the 1-

hour NAAQS for SO2 

Acceptable Impact 

(NAAQS - Background) 

99th Percentile 

1-hour Daily Max 

(μg/m3

) 

Required 

Total Facility 

Reduction Based on 

Allowable Emissions 

(%) 

Required 

Total Facility 

Emission Rate 

(lbs/hr) 

Required 

Total Facility 

1-hour Average 

Emission Rate 

(lbs/mmbtu) 

193.6 65% 3,457.2 0.11 

2.3 Conservative Modeling Assumptions 

A dispersion modeling analysis requires the selection of numerous parameters which affect the 

predicted concentrations. For the enclosed analysis, several parameters were selected which underpredict facility impacts. 

Assumptions used in this modeling analysis which likely under-estimate concentrations include the 

following: 

 Allowable emissions are based on a limitation with an averaging period which is greater than 

the 1-hour average used for the SO2 air quality standard. Emissions and impacts during any 

1-hour period may be higher than assumed for the modeling analysis. 

 No consideration of facility operation at less than 100% load. Stack parameters such as exit 

flow rate and temperature are typically lower at less than full load, reducing pollutant 

dispersion and increasing predicted air quality impacts. 

 No consideration of building or structure downwash. These downwash effects typically 

increase predicted concentrations near the facility. 

 Except for the five other power plants and the US Steel facility, no consideration of off-site 

sources. Any other off-site sources of SO2 will increase the predicted impacts.
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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Figure 1 - Regional View of Impacts Based on Allowable Emissions from All Six Power Plants
Evaluation of Compliance with the 1-hour NAAQS for SO2

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Figure 2 - Regional View of Impacts Based on Actual Emissions from All Facilities 

 
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3. Modeling Methodology 

3.1 Air Dispersion Model 

The modeling analysis used USEPA’s AERMOD program, v. 14134. AERMOD, as available from 

the Support Center for Regulatory Atmospheric Modeling (SCRAM) website, was used in 

conjunction with a third-party modeling software program, AERMOD View, sold by Lakes 

Environmental Software. 

3.2 Control Options 

 

The AERMOD model was run with the following control options: 

 1-hour average air concentrations 

 Regulatory defaults 

 Flagpole receptors 

To reflect a representative inhalation level, a flagpole height of 1.5 meters was used for all modeled 

receptors. This parameter was added to the receptor file when running AERMAP, as described in 

Section 4.4. 

An evaluation was conducted to determine if the modeled facility was located in a rural or urban 

setting using USEPA’s methodology outlined in Section 7.2.3 of the Guideline on Air Quality 

Models.7

 For urban sources, the URBANOPT option is used in conjunction with the urban 

population from an appropriate nearby city and a default surface roughness of 1.0 meter. Methods 

described in Section 4.1 were used to determine whether rural or urban dispersion coefficients were 

appropriate for the modeling analysis. 

 

3.3 Output Options 

The AERMOD analysis was based on three years of recent meteorological data. The modeling 

analyses used one run with three years of sequential meteorological data from 2012-2014. Consistent 

with USEPA’s Modeling Guidance for SO2 NAAQS Designations, AERMOD provided a table of 

fourth-high 1-hour SO2 impacts concentrations consistent with the form of the 1-hour SO2 NAAQS.8 

Please refer to Table 1 for the modeling results. 

 

7

 USEPA, Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex 

Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, November 9, 2005.

8 USEPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24, 2011, pp. 24-26. 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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4. Model Inputs 

4.1 Geographical Inputs 

The “ground floor” of all air dispersion modeling analyses is establishing a coordinate system for 

identifying the geographical location of emission sources and receptors. These geographical 

locations are used to determine local characteristics (such as land use and elevation), and also to 

ascertain source to receptor distances and relationships. 

The Universal Transverse Mercator (UTM) NAD83 coordinate system was used for identifying the 

easting (x) and northing (y) coordinates of the modeled sources and receptors. Stack locations were 

obtained from facility permits and prior modeling files provided by the state regulatory agency. The 

stack locations were then verified using aerial photographs. 

The facility was evaluated to determine if it should be modeled using the rural or urban dispersion 

coefficient option in AERMOD. A Geographic Information System (GIS) was used to determine 

whether rural or urban dispersion coefficients apply to a site. Land use within a three-kilometer 

radius circle surrounding the facility was considered. USEPA guidance states that urban dispersion 

coefficients are used if more than 50% of the area within 3 kilometers has urban land uses. 

Otherwise, rural dispersion coefficients are appropriate.9

 

USEPA’s AERSURFACE v. 13016 was used to develop the meteorological data for the modeling 

analysis. This model was also used to evaluate surrounding land use within 3 kilometers. Based on 

the output from the AERSURFACE, approximately 9.9% of surrounding land use around the 

modeled facility was of urban land use types including Type 21 – Low Intensity Residential, Type 

22 – High Intensity Residential and Type 23 – Commercial / Industrial / Transportation. 

This is less than the 50% value considered appropriate for the use of urban dispersion coefficients. 

Based on the AERSURFACE analysis, it was concluded that the rural option would be used for the 

modeling summarized in this report. Please refer to Section 4.5.3 for a discussion of the 

AERSURFACE analysis.

 

 

9

 USEPA, Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex 

Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, November 9, 2005, Section 7.2.3. 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

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4.2 Emission Rates and Source Parameters 

The modeling analysis considered SO2 emissions from Monroe, five other power plants, and one 

industrial facility. Other off-site sources were not considered. Concentrations were predicted for the 

scenarios shown in Tables 1 and 2: 

1) allowable emissions based on the current permit issued by the regulatory agency, and 

2) for the six power plants actual hourly emissions measured each hour between January 1, 

2012 and December 31, 2014 as taken from USEPA Air Markets Program Data.

10 For the 

industrial facility, US Steel, actual emissions are the annual average of emissions reported for 

calendar year 2014. 

Stack parameters and emissions used for the modeling analysis are summarized in Table 4. 

The stack parameters and emissions were obtained from regulatory agency documents and databases 

identified in Section 2.2. The analysis was conducted based on 100% operating load using maximum 

exhaust flow rates and temperatures. Operation at less than full capacity loads was not considered. 

This assumption tends to under-predict impacts since stack parameters such as exit flow rate and 

temperature are typically lower at less than full load, reducing pollutant dispersion and increasing 

predicted air quality impacts. Stack location, height and diameter were verified using aerial 

photographs, and flue gas flow rate and temperature were verified using combustion calculations. 

 

10 http://ampd.epa.gov/ampd/ 
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Table 4 – Facility Stack Parameters and Emissions 11

Facility Stack Description X Coordinate [m] Y Coordinate [m] Base Elevation [m] Release Height [m] Exit Temperature [K] Exit Velocity [m/s] Inside Diameter [m] 

Monroe 

M01 Unit 1 305534 4640274 175.71 176.48 325.928 39.624 6.309 

M02 Unit 2 305538 4640278 175.92 176.48 325.928 39.624 6.309 M03 Unit 3 305379 4640207 177.27 176.48 325.928 39.624 6.309 M04 Unit 4 305385 4640211 177.25 176.48 325.928 39.624 6.309 

Trenton 

T01 Units 16 to 19 319707 4665685 177.39 170.38 427.59 42.672 4.42 

T09 Unit 9A 319740 4665610 177.28 171.15 410.93 42.672 4.877 

River Rouge 

R02 Unit 2 325806 4682363 175.03 117.35 420.93 48.768 3.665 

R03 Unit 3 325771 4682374 175.06 129.54 433.15 48.768 3.911 

J.R. Whiting 

J01 Boiler 1 296512 4629557 176.98 90.53 414.261 16.982 3.231 

J02 Boiler 2 296512 4629576 176.91 90.53 417.039 17.903 3.231 J03 Boiler 3 296512 4629596 176.92 90.53 426.483 11.665 3.523 

Bay Shore B01 Unit B006 297140 4618518 177.07 91.44 423.706 24.659 3.658 

Wyandotte 

W07 Unit 7 322901 4675118 175.15 52.73 413.706 8.47 2.794 

W08 Unit 8 322853 4675144 176.51 65.53 435.928 10.71 1.981 

US Steel 

SV001 Coke Battery 325930.8 4683222 177.32 14.63 294.261 21.105 0.509 

SV003 Hot Strip Mill 326024.8 4683094 177.06 34.75 366.483 10.349 3.048 SV007 A Furnace 325549.8 4681690 175.29 31.09 477.594 1.617 4.267 

SV0013 D Baghouse 326107.8 4683835 176.6 33.22 544.261 21.184 1.396 SV0017 D Stove 326179.8 4683430 177.04 20.73 294.261 15.25 3.292 SV0018 No. 2-1 Boiler 326207.8 4683389 176.96 70.1 560.928 13.531 2.819 SV0020 No. 1-1 Boiler 326326.8 4683772 176.45 20.73 560.928 17.106 1.676 SV0025 No. 2-1 Boiler 326278.8 4683326 176.77 26.82 560.928 7.484 2.972 

11 Monroe, River Rouge, Trenton Channel, Wyandotte and Whiting stack parameters obtained from USEIA, 2012 Form EIA-860 Data - S

http://www.eia.gov/electricity/data/eia860/. Bay Shore stack parameters obtained from OEPA, Facility Profile Report, September 8, 2015. U

actual emissions obtained from MDEQ, Michigan Air Emissions Reporting System (MAERS) for 2014. 
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September 16, 2015 

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4.3 Building Dimensions 

No building dimensions or prior downwash evaluations were available. Therefore this modeling analysis 

did not address the effects of downwash and this may under-predict impacts. 

4.4 Receptors 

For Monroe Power Plant, three receptor grids were employed: 

1. A 100-meter Cartesian receptor grid centered on Monroe Power Plant and extending out 5 

kilometers. 

2. A 500-meter Cartesian receptor grid centered on Monroe Power Plant and extending out 10 

kilometers. 

3. A 1,000-meter Cartesian receptor grid centered on Monroe Power Plant and extending out 50 

kilometers. 50 kilometers is the maximum distance accepted by USEPA for the use of the 

AERMOD dispersion model.12

A flagpole height of 1.5 meters was used for all these receptors. 

Elevations from stacks and receptors were obtained from National Elevation Dataset (NED) GeoTiff 

data. GeoTiff is a binary file that includes data descriptors and geo-referencing information necessary for 

extracting terrain elevations. These elevations were extracted from 1 arc-second (30 meter) resolution 

NED files. The USEPA software program AERMAP v. 11103 is used for these tasks. 

4.5 Meteorological Data 

To improve the accuracy of the modeling analysis, recent meteorological data for the 2012-2014 period 

were prepared using the USEPA’s program AERMET which creates the model-ready surface and profile 

data files required by AERMOD. Required data inputs to AERMET included surface meteorological 

measurements, twice-daily soundings of upper air measurements, and the micrometeorological 

parameters surface roughness, albedo, and Bowen ratio. One-minute ASOS data were available so 

USEPA methods were used to reduce calm and missing hours.13 The USEPA software program 

AERMINUTE v. 14237 is used for these tasks. 

For this modeling project, pre-processed meteorological data were provided by the Michigan Department 

of Environmental Quality (DEQ).14, 15 Data for the 2012 to 2013 period were downloaded from the DEQ 

 

12 USEPA, Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex 

Terrain) Dispersion Model and Other Revisions, Appendix W to 40 CFR Part 51, Section A.1.(1), November 9, 2005. 

13 USEPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24, 2011, p. 19. 

14 Michigan Department of Environmental Quality, Map of Available Meteorological Stations, 

http://www.michigan.gov/documents/deq/deq-aqd-mm-met_support_256121_7.pdf 
Evaluation of Compliance with the 1-hour NAAQS for SO2

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web site and data for the 2014 period were provided directly by DEQ. The agency prepared its 

meteorological data using the procedures described in this report. 

This section discusses how the meteorological data was prepared for use in the 1-hour SO2 NAAQS 

modeling analyses. The USEPA software program AERMET v. 14134 is used for these tasks. 

4.5.1 Surface Meteorology 

Surface meteorology was obtained for Custer Airport located near the Monroe Power Plant. Integrated 

Surface Hourly (ISH) data for the 2012-2014 period were obtained from the National Climatic Data 

Center (NCDC). The ISH surface data was processed through AERMET Stage 1, which performs data 

extraction and quality control checks. 

4.5.2 Upper Air Data 

Upper-air data are collected by a “weather balloon” that is released twice per day at selected locations. 

As the balloon is released, it rises through the atmosphere, and radios the data back to the surface. The 

measuring and transmitting device is known as either a radiosonde, or rawindsonde. Data collected and 

radioed back include: air pressure, height, temperature, dew point, wind speed, and wind direction. The 

upper air data were processed through AERMET Stage 1, which performs data extraction and quality 

control checks. 

For Monroe Power Plant, the concurrent 2012-2014 upper air data from twice-daily radiosonde 

measurements obtained at the most representative location were used. This location was the White Lake, 

Michigan measurement station. These data are in Forecast Systems Laboratory (FSL) format and were 

downloaded in ASCII text format from NOAA’s FSL website.16 All reporting levels were downloaded 

and processed with AERMET. 

4.5.3 AERSURFACE 

AERSURFACE is a program that extracts surface roughness, albedo, and daytime Bowen ratio for an 

area surrounding a given location. AERSURFACE uses land use and land cover (LULC) data in the U.S. 

Geological Survey’s 1992 National Land Cover Dataset to extract the necessary micrometeorological 

data. LULC data was used for processing meteorological data sets used as input to AERMOD. 

AERSURFACE v. 13016 was used to develop surface roughness, albedo, and daytime Bowen ratio 

values in a region surrounding the meteorological data collection site. AERSURFACE was used to 

 

15 Email from J. Haywood – MDEQ to S. Klafka – Wingra Engineering, S.C., Request for AERMOD Modeling Meteorology 

for Michigan Power Plants, May 18, 2015. 

16 Available at: http://esrl.noaa.gov/raobs/ 
Evaluation of Compliance with the 1-hour NAAQS for SO2

September 16, 2015 

Page 15 

develop surface roughness in a one kilometer radius surrounding the data collection site. Bowen ratio 

and albedo was developed for a 10 kilometer by 10 kilometer area centered on the meteorological data 

collection site. 

4.5.4 Data Review 

Missing meteorological data were not filled as the data file met USEPA’s 90% data completeness 

requirement.17 The AERMOD output file shows there were 2.1% missing data. 

To confirm the representativeness of the airport meteorological data, the surface characteristics of the 

airport data collection site and the modeled source location were compared. Since the Custer Airport is 

located close to Monroe Power Plant, this meteorological data set was considered appropriate for this 

modeling analysis. 18 This weather station provided high quality surface measurements for the most 

recent 3-year time, and had similar land use, surface characteristics, terrain features and climate. Finally, 

DEQ provided pre-processed meteorological data for this project and had concluded that the weather 

stations were representative of the project location. 

5. Background SO2 Concentrations 

Background concentrations were determined consistent with USEPA’s Modeling Guidance for SO2

NAAQS Designations.19, 20 To preserve the form of the 1-hour SO2 standard, based on the 99th percentile 

of the annual distribution of daily maximum 1-hour concentrations averaged across the number of years 

modeled, the background fourth-highest daily maximum 1-hour SO2 concentration was added to the 

modeled fourth-highest daily maximum 1-hour SO2 concentration.21 Background concentrations were 

based on the 2011-13 design value measured by the ambient monitors located in Michigan.22 

6. Reporting 

All files from the programs used for this modeling analysis are available to regulatory agencies. These 

include analyses prepared with AERSURFACE, AERMET, AERMAP, and AERMOD. 

 

17 USEPA, Meteorological Monitoring Guidance for Regulatory Modeling Applications, EPA-454/R-99-05, February 2000, 

Section 5.3.2, pp. 5-4 to 5-5. 

18 USEPA, AERMOD Implementation Guide, March 19, 2009, pp. 3-4. 

19 USEPA, Area Designations for the 2010 Revised Primary Sulfur Dioxide National Ambient Air Quality Standards, 

Attachment 3, March 24, 2011, pp. 20-23. 

20 USEPA, SO2 NAAQS Designations Modeling Technical Assistance Document, Dec. 2013, section 8.1, pp 27-28. 21 USEPA, Applicability of Appendix W Modeling Guidance for the 1-hour SO2 National Ambient Air Quality Standard, 

August 23, 2010, p. 3. 

22 http://www.epa.gov/airtrends/values.html